InAs quantum dots on nanopatterned GaAs (001) surface: the growth, optical properties, and device implementation

This work reviews the growth, optical properties, and device implementation of InAs semiconductor quantum dots (QDs) selectively nucleated atop nano-faceted GaAs pyramidal structures grown by metal-organic chemical-vapor deposition. This site-controlled QD growth technique offers unique features and benefits subsequent device applications. First, GaAs pyramids, formed on a SiO2-masked and nanopatterned (001) GaAs substrate, are characterized by well-defined equilibrium crystal shapes (ECS). The controlled ECS formation is crucial to subsequent patterned QD (PQD) nucleation, which is highly preferential toward {11n} planes due to superior QD energy minimization. Second, PQD optical properties are thoroughly studied by monitoring room temperature (RT) photoluminescence (PL) and power-dependent low-temperature PL to verify the crystalline quality and the three-dimensional quantum confinement. The PQD ensembles formed on different GaAs pyramids, with different PL behavior, indicate lateral coupling within QD clusters and characteristics of isolated QD pairs. Then, PQDs embedded in a InGaAs quantum well, the so-called dot-in-the-well (DWELL) structure, are compared to a self-assembled QD (SAQD) DWELL structure, and shown to have a better emission efficiency, due to the distributed QW thickness profile on the faceted GaAs pyramid. Finally, broad-area light emitting diodes based on the PQD active region are fabricated. Linear current-voltage characteristics are observed with sharp turn-on, low leakage current and low forward resistance. Electroluminescence spectra show PQD intraband structure and low quenching of emission from 77 K to room temperature. Light-current measurements demonstrate external quantum efficiency per PQD comparable to SAQDs, despite the two regrowth steps in the fabrication processes.